Rename image* to cover*

lib/obsidian/entry.ex

@@ -1,3 +1,3 @@
 defmodule Obsidian.Entry do
-  defstruct [:type, :musicbrainz_id, :title, :release, :image_url, :genres]
+  defstruct [:type, :musicbrainz_id, :title, :release, :cover_url, :genres]
 end

lib/obsidian/parser.ex

@@ -9,7 +9,7 @@ defmodule Obsidian.Parser do
          musicbrainz_id: meta["id"],
          title: meta["title"],
          release: meta["year"] |> parse_release(),
-         image_url: meta["image"],
+         cover_url: meta["image"],
          genres: meta["genres"]
        }}
     end